CH. Ill] BRANCHING 35 



on this may be termed secondary axes, but in their turn 

 primary with regard to branches they themselves bear. We 

 thus come to regard branches as of various degrees or 

 orders, and speak of a primary axis bearing branches of the 

 first order, any of which may bear branches of the second 

 order, these branches of the third order, and so on to 

 any extent, as exhibited by the ramification of most trees 

 into limbs, branches and twigs. Or we may speak of 

 primary, secondary, tertiary, &c. branches. 



It will thus be seen that when we find a stem bearing 

 leaves only, our reason for not calling this a branched 

 stem is that the lateral appendages (leaves) are not of 

 like kind, and it would appear to be a very simple matter 

 to determine every case by direct observation were it not 

 that comparison shows that careful examination is fre- 

 quently necessary to decide whether a given lateral 

 appendage is or is not fundamentally similar to the axis 

 producing it. 



In the case of the typical branches of ordinary stems 

 or roots no difficulty arises. Each primary root developes 

 secondary roots, of like kind, and each secondary root 

 may develope tertiary roots in like manner, and so on ; 

 and it is characteristic of typical roots that they only 

 bear lateral organs of like kind i.e. they branch, but do 

 not develope other appendages. 



With the shoot-system matters are more complicated, 

 however, in accordance with its more variable environment. 

 Not only does it support very different kinds of ap- 

 pendages, especially leaves and their modifications and 

 the reproductive organs, but its branches undergo so 

 many alterations in form, position and relations of various 

 kinds, that we have sometimes to be on the look-out for 

 very definite criteria to guide us in determining what 

 are and what are not branches. 



32 



